Arch shape molded plastic storm chambers, such commercial StormTech Model SC310 and SC740 chambers (StormTech, LLC, Wethersfield, Conn.), are typically connected together end-to-end as strings. In a typical installation, an array of parallel rows of chambers is placed on a bed of gravel within a pit, and is then covered with layers of gravel and other material, such as soil or paving. During a storm, surface water which runs to catch basins is then channeled to the chambers, where it is received and detained. The water may be later discharged from the storm chamber array by percolation into the surrounding earth, or by flowing as runoff to a stream or the like. The ends of the chamber strings must be capped to prevent entry of the gravel or other particulate medium which surrounds the chambers. In the past, open-ended chambers used for stormwater have often been closed with flat or planar end-caps. The aforementioned StormTech chambers have been sold with end caps that have a convex exterior curve, often referred to as a dome shape.
A preferred way of conveying water to or from buried chambers is to run pipes through holes cut in the end caps. Common commercial pipes are made of polyethylene and may be corrugated or plain. Typically, to connect a pipe to an end cap, an installer cuts a hole in the end cap in the field, to the approximate size of the pipe which may range in outside diameter from 4 to 12 inches, or larger. He then inserts the pipe into the hole, so it projects into the chamber interior for what seems a suitable distance, for example 6 inches or more.
To facilitate the field-cutting of holes, the exterior surfaces of end caps have been provided with various-diameter embossed areas, to guide the installer where to cut. However, it is a problem that the installer does not do a good job in making the cut hole fit the pipe. With the preferred convex dome shape end cap, the hole has to be a curved ellipse, precluding the use of a circle cutter which might be used on a planar end cap. That has presented judgment problems as to the configuration of the hole, especially if the pipe entry location does not correspond with the manufacturer-provided embossing, or if the pipe runs at a horizontal or vertical plane angle to the length of the chamber. Another problem is that the installer may not have proper tools and may be working under adverse weather conditions. Those factors often result in gaps between the end cap wall and the pipe outside diameter, which can enable finer sized granular medium to enter the chamber.
When the pipe is corrugated, as is often the case, then some gap is inevitable. This can be understood from FIG. 3. The dashed line 27 indicates how the cut edge of the dome 23 of end cap 18 contacts the corrugated pipe 22A. It will be appreciated that, because of the valleys of the corrugation, no matter how good a job is done in making the curved ellipse hole, there will still be a path for entry of media. Furthermore, when the pipe is put in place in the hole, if the bottom of the pipe is supported by a valley corrugation, as will likely happen, the pipe will lie eccentrically in the hole, with a gap at the top. That can allow granular medium, particularly finer particles, to enter the chamber through the gaps. The storage capacity of the storm chamber system can be compromised, and there might be some subsidence of the overlying material.
Another problem, particularly when the pipe diameter is large relative to the size of the end cap and associated chamber, is that a large hole in the end cap might significantly decrease the structural integrity of the cap and is capacity to resist the inward force of the surrounding media.